Mechanical Ventilation with Heat Recovery Unit
People and electrical appliances generate heat, it is used again by the ventilation system by preheating the incoming clean air before blowing off the foul air.
The amount of energy required to air-condition spaces is so little that it could be covered by using a small heater without having a conventional radiator or radiant floor system, with the subsequent financial saving involved.
In a Passivhaus building, with an air flow of fresh air of around 1/3 of the spaces volume, around 10 W/m of heat and 7 W/m² of cold can be provided in the building, fixing a ceiling on heating and cooling demand of around 15 kWh/(m²a).
In conventional buildings the draughts through windows, gaps or cracks cause user discomfort and even inside condensation, particularly during the coldest periods of the year.
In a Passivhaus building the envelope is as airtight as possible, achieving high efficiency of the mechanical ventilation system. This is achieved by paying maximum attention to seals on windows and doors during installation.
The building's airtightness is measured by carrying out a pressure or Blower Door test, which consists on creating a pressure difference between inside and outside through a fan located at the main door. To meet the standard, the result must be lower that 0,6 air changes per hour